The present disclosure relates generally to medical fluid delivery systems and methods. This disclosure includes systems and methods for calculating a peritoneal dialysis therapy that will yield one or more favorable outcomes for a patient. In particular, the disclosure concerns calculating a series of dialysis outcomes using a series of dialysis variables with a digital computer and a computer program.
Due to various causes, a person's renal system can fail. Renal failure produces several physiological impairments and difficulties. The balance of water, minerals and the excretion of daily metabolic load is no longer possible and toxic end products of nitrogen metabolism (urea, creatinine, uric acid, and others) can accumulate in blood and tissue. Kidney failure and reduced kidney function have been treated with dialysis. Dialysis removes waste, toxins and excess water from the body that would otherwise have been removed by normal functioning kidneys. Dialysis treatment for replacement of kidney functions is critical to many people because the treatment is life saving.
Hemodialysis and peritoneal dialysis are two types of dialysis therapies used commonly to treat loss of kidney function. A hemodialysis (“HD”) treatment utilizes the patient's blood to remove waste, toxins and excess water from the patient. The patient is connected to a hemodialysis machine and the patient's blood is pumped through the machine. Catheters are inserted into the patient's veins and arteries so that blood can flow to and from the hemodialysis machine. The blood passes through a dialyzer of the machine, which removes waste, toxins and excess water from the blood. The cleaned blood is returned to the patient. A large amount of dialysate, for example about 120 liters, is consumed to dialyze the blood during a single hemodialysis therapy. Hemodialysis treatment lasts several hours and is generally performed in a treatment center about three or four times per week.
Another form of kidney failure treatment involving blood is hemofiltration (“HF”), which is an alternative renal replacement therapy that relies on a convective transport of toxins from the patient's blood. This therapy is accomplished by adding substitution or replacement fluid to the extracorporeal circuit during treatment (typically ten to ninety liters of such fluid). That substitution fluid and the fluid accumulated by the patient in between treatments is ultrafiltered over the course of the HF treatment, providing a convective transport mechanism that is particularly beneficial in removing middle and large molecules.
Hemodiafiltration (“HDF”) is another blood treatment modality that combines convective and diffusive clearances. HDF uses dialysate to flow through a dialyzer, similar to standard hemodialysis, providing diffusive clearance. In addition, substitution solution is provided directly to the extracorporeal circuit, providing convective clearance.
Peritoneal dialysis uses a dialysis solution, also called dialysate, which is infused into a patient's peritoneal cavity via a catheter. The dialysate contacts the peritoneal membrane of the peritoneal cavity. Waste, toxins and excess water pass from the patient's bloodstream, through the peritoneal membrane and into the dialysate due to diffusion and osmosis, i.e., an osmotic gradient occurs across the membrane. The spent dialysate is drained from the patient, removing waste, toxins and excess water from the patient. This cycle is repeated.
Peritoneal dialysis machines are used to accomplish this task. Such machines are described, for example, in the following U.S. patents, all of which are incorporated by reference in their entirety, as though each patent were set forth herein, page by page, in its entirety: U.S. Pat. Nos. 5,350,357; 5,324,422; 5,421,823; 5,431,626; 5,438,510; 5,474,683; 5,628,908; 5,634,896; 5,938,634; 5,989,423; 7,153,286; and 7,208,092.
There are various types of peritoneal dialysis therapies, including continuous ambulatory peritoneal dialysis (“CAPD”), automated peritoneal dialysis (“APD”), tidal flow APD and continuous flow peritoneal dialysis (“CFPD”). CAPD is a manual dialysis treatment. The patient manually connects an implanted catheter to a drain, allowing spent dialysate fluid to drain from the peritoneal cavity. The patient then connects the catheter to a bag of fresh dialysate, infusing fresh dialysate through the catheter and into the patient. The patient disconnects the catheter from the fresh dialysate bag and allows the dialysate to dwell within the peritoneal cavity, wherein the transfer of waste, toxins and excess water takes place. After a dwell period, the patient repeats the manual dialysis procedure, for example, four times per day, each treatment lasting about an hour. Manual peritoneal dialysis requires a significant amount of time and effort from the patient, leaving ample room for improvement. In particular there is room for improvement in the selection of dwell times for the patient.
Automated peritoneal dialysis (“APD”) is similar to CAPD in that the dialysis treatment includes drain, fill, and dwell cycles. APD machines, however, perform the cycles automatically, typically while the patient sleeps. APD machines free patients from having to manually perform the treatment cycles and from having to transport supplies during the day. APD machines connect fluidly to an implanted catheter, to a source or bag of fresh dialysate and to a fluid drain. APD machines pump fresh dialysate from a dialysate source, through the catheter, into the patient's peritoneal cavity, and allow the dialysate to dwell within the cavity, and allow the transfer of waste, toxins and excess water to take place. The source can be multiple sterile dialysate solution bags.
APD machines pump spent dialysate from the peritoneal cavity, though the catheter, to the drain. As with the manual process, several drain, fill and dwell cycles occur during APD. A “last fill” occurs at the end of CAPD and APD, which remains in the peritoneal cavity of the patient until the next treatment.
Both CAPD and APD are batch type systems that send spent dialysis fluid to a drain. Tidal flow systems are modified batch systems. With tidal flow, instead of removing all of the fluid from the patient over a longer period of time, a portion of the fluid is removed and replaced after smaller increments of time.
Continuous flow, or CFPD, systems clean or regenerate spent dialysate instead of discarding it. These systems pump fluid into and out of the patient, through a loop. Dialysate flows into the peritoneal cavity through one catheter lumen and out another catheter lumen. The fluid exiting the patient passes through a reconstitution device that removes waste from the dialysate, e.g., via a urea removal column that employs urease to enzymatically convert urea into ammonia. The ammonia is then removed from the dialysate by adsorption prior to reintroduction of the dialysate into the peritoneal cavity. Additional sensors are employed to monitor the removal of ammonia. CFPD systems are typically more complicated than batch systems.
In each of the kidney failure treatment systems discussed above, it is important to control ultrafiltration, which is the process by which water (with electrolytes and other neutral solutes) moves across a membrane, such as a dialyzer or peritoneal membrane. For example, ultrafiltration in peritoneal dialysis is a result of osmotic and hydrostatic pressure differences between blood and dialysate across the patient's peritoneal membrane. It is also important to control the concentration of metabolic substances in the patient's bloodstream, such as urea concentration, β2-microglobulin, creatinine concentration, and so forth. Each of these, along with many other variables, constitutes a peritoneal dialysis outcome.
Each patient is different, possessing for instance, a unique peritoneal membrane, its own separation characteristics, and its unique response to peritoneal dialysis. Each patient is also different with respect to body surface area (BSA) and total body water volume, which also have an effect on transport characteristics. Each patient is different in terms of transport characteristics that relate to the ultrafiltration rate. Each patient is also different in terms of response to dialysis, that is, the amount of water and waste removed in a given time period, using a given fill volume, a particular dialysis fluid, and so forth.
One basic difference among patients is the rate at which water and metabolic wastes pass from the patient's bloodstream through the peritoneal membrane. Once the water and wastes pass through the peritoneal membrane, they are absorbed into the dialysis therapy fluid that has been placed into the patient's peritoneal cavity, and then removed from the patient. A peritoneal equilibration test (PET) determines the relative rate of transmembrane transport. Patients can then be classified as high-rate transporters, high-average transporters, low-average transporters, or low-rate transporters, depending on the speed of waste removal and absorption of glucose from the dialysis fluid. Other user classes may also be used, such as high, average, and low transporters. Patients may also be classified in terms of their total body surface area (“BSA”), which depends only on the height and weight of the patient.
In general, the rate of water removal is different from the rate of waste removal, and both depend on the patient transporter type and is indirectly related to patient membrane transport type. For example, fast transporters can quickly pass metabolic waste, but glucose from the dialysis solution is rapidly absorbed into the body. As a result, glucose concentration in the dialysate decreases and the osmotic gradient or driving force diminishes within a variable period of time, depending on the patient transporter type. Thus, high transporters may benefit more from shorter dwell times, such as those used in automated peritoneal dialysis (APD), where the effect of high osmotic gradients is still present.
Conversely, the osmotic gradient will be sustained for a longer period of time in the case of a low transporter patient, resulting in a larger volume of ultrafiltrate removal. Such a patient will likely benefit from a longer dwell time, such as a continuous ambulatory peritoneal dialysis (CAPD) and with perhaps only a single nighttime exchange. Much useful information about a patient's response to therapy can be learned from administering the PET to the patient. The results of the PET can then be used to prescribe the therapy that would lead to the best outcome for that patient.
However, present PET tests require long periods of time to administer and also typically require at least one blood sample for confirmation of the level of certain waste products in the patient's blood, such as creatinine, to be sure that dialysis therapy being administered is indeed effective. Thus, while the PET test can be valuable in deciding the general characteristics of a patient, the difficulty in administering a PET test may be a significant barrier in determining the therapy best suited for a patient.
This may be particularly true in a patient suffering from unplanned or acute renal failure. Acute renal failure can occur in an emergency situation, such as a car accident, in which the patient loses renal function. In these cases, it is clear that the patient is suffering and requires dialysis quickly. Without some guidance on which peritoneal dialysis treatment to use, such a patient may be prematurely routed to hemodialysis rather than more convenient and less costly peritoneal dialysis. What is needed is a better way to select a peritoneal dialysis therapy that is suited to a patient that needs dialysis in an unplanned situation.